1. Field of the Invention
The present invention relates to an apparatus for recording and reproducing information on a magnetic disk, and more precisely, to a magnetic disk recording and reproducing apparatus which has a position adjusting servo-mechanism for a magnetic recording and reproducing head in the apparatus.
2. Description of Related Art
In conventional magnetic disk recording and reproducing apparatus such as an electronic still camera or a floppy disk drive, a magnetic head is moved in radial directions of the magnetic disk in a stepped fashion by an intermittently moving device, to successively trace a large number of concentric recording tracks.
FIG. 7 shows, in from elevation the internal construction of a known magnetic disk recording and reproducing apparatus.
In FIG. 7, a recording and reproducing magnetic head 10 is secured to a generally L-shaped carriage 12 through a piezoelectric element 11. The piezoelectric element 11 comprises a number of laminated piezoelectric plate elements, so that when a voltage is applied between terminal electrodes of the piezoelectric element 11, the latter deforms in thickness l thereof, depending on the polarity and value of the voltage.
A carriage 12 is slidably attached to parallel guide rods 14 and 15 provided on a body 13 of the magnetic recording and reproducing apparatus so as to move the magnetic head 10 along the guide rods. The direction of movement of the carriage 12 corresponds to the direction of movement of the magnetic head 10 which moves above and along the plane of a magnetic disk D, which is supported by a rotational shaft 17 of a magnetic disk driving motor 16, in the radial directions of the magnetic disk. The guide rod 14 is provided with a compression coil spring 18 which is wound around the guide rod 14 to continuously bias the carriage 12 so as to urge the latter far away from the magnetic disk driving motor 16.
Above the carriage 12 in FIG. 7, is a plate cam 20 rotatably mounted to the body 13 through a shaft 22. The plate cam 20 has a peripheral cam surface 21 against which a pin 19, provided on the carriage 12, abuts with the help of the compression coil spring 18. The plate cam 20 has a ratchet gear 23 and a click gear 30 which are both coaxial to the plate cam 20 so as to rotate together.
The ratchet gear 23 is engaged by a pawl 24a which is formed on the front end of a feed lever 24. The feed lever 24 has an elongated hole 24b which is formed at an intermediate portion thereof and which extends substantially in parallel with the guide rod 14. A pin 25, which is provided on the body 13, is fitted in the elongated hole 24b, so that the feed lever 24 can rotate and linearly move. The linear movement of the feed lever 24 is performed by a plunger solenoid 26 which is rotatably connected to the lower end of the feed lever in FIG. 7. The feed lever 24 is continuously biased by a tension spring 27 which is provided between and connected to a pin 13a provided on the body 13 and an arm 24c which is formed on the feed lever 24, so that the ratchet pawl 24a is urged into engagement with the ratchet wheel 23. Thus, when the plunger solenoid 26 is activated with one pulse, one reciprocal movement of the feed lever 24 in the direction parallel with the guide rod 14 takes place to rotate the ratchet wheel 23 by one pitch corresponding to one tooth of the ratchet gear 23 in the clockwise direction in FIG. 7. Numerals 28 and 29 designate stop pins which are provided on the body 13 to restrict the upper and lower terminal ends of the movement of the feed lever 24.
A click gear 30 is engaged by a click pawl 31a which is formed at the front end of a click lever 31 to stop the rotation of the click gear 30 and accordingly, the plate cam 20 at every pitch (tooth) of the click gear 30. The click lever 31 is pivoted at its rear end to a body 13 through a shaft 32 and has a torsion spring 33 provided between the click lever 31 and the body 13 to bias the click lever 31, so that the click pawl 31a comes into engagement with the click gear 30. The click pawl 31a successively comes into the tooth grooves between the tooth threads of the click gear 30 when the click gear 30 rotates in the clockwise direction to intermittently hold the click gear at a predetermined pitch.
The apparatus shown in FIG. 7 operates as follows.
Upon recording and reproducing the magnetic disk D, the plunger solenoid 26 is actuated a predetermined number of times to rotate the plate cam 20 by a predetermined angular displacement in the clockwise direction in order to move the carriage 12, so that the magnetic head 10 is brought into a predetermined position in which the magnetic head 10 is located above a desired track of the magnetic disk D. This position will be referred to as an on-track position. The position of the magnetic head 10 is determined in accordance with the angular position of the plate cam 20, which is restricted by the engagement of the ratchet pawl 24a in the ratchet gear 23.
In the known apparatus mentioned above, the magnetic head can not usually be stopped at a constant and desired position (on-track position) due to mechanical and physical errors of the head actuating mechanism and the magnetic disk, etc., as shown in FIG. 4. In FIG. 4, the abscissa represents the track number, and the ordinate represents the deviation, i.e. the amount of off-track of the magnetic head from a reference position. As shown in FIG. 4, the magnetic head can not be precisely brought into the on-track position, resulting in read errors, especially when a recording and reproducing are performed by different machines.
To eliminate the problem mentioned above, the piezoelectric element 11 serves as a servo-mechanism for adjusting the position of the magnetic head. The piezoelectric element 11 changes in thickness l thereof in accordance with the direction of the current flow and the voltage is provided between the magnetic head 10 and the carriage 12, so as to realize an accurate on-track positioning.
However, since the deformation of the piezoelectric element is very small, it is necessary to use a thick and large piezoelectric element in order to provide a sufficient deformation (displacement). This results in a large magnetic disk recording and reproducing apparatus.
It is also possible to increase the number of teeth of the click gear to realize a fine adjustment servo-mechanism of the magnetic head. This solution however, is not desirable, since, first it is very difficult to manufacture a small click gear having a large number of teeth, and second, since it is necessary to increase the diameter of the click gear, resulting in the need to use of a reduction gear.